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TR4/4A TR4A ignition switch question

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tdskip

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Hi guys - the Moss catalog only lists a single part number for the TR4 / TR4a ignition switch but I believe the TR4 has a 3 post configuration and the TR4A has a 4 post.

Can you use a TR4 3 post with a TR4a harness? If so where would you connect the light/green wire on the 3 post?

Thanks!
 
According to my factory parts books, they are the same switch. So I'm guessing that the TR4 just didn't use one of the extra terminals.

I also don't see a light/green wire on any of the 4A schematics, so I can't help there. What does it go to?
 

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I just bought one for my 4a and it has at least two extra terminals.
 
OK - do here is the behavior I am seeing (which may/may not be related to my missing #4 post on the ignition switch).

I can use the solenoid to bump the engine over by using the manual switch in the engine bay, but turning the key doesn't result in anything.

When I put a test lamp on the white/red wire and turn the key it lights up when I turn the key all the way.

Ideas?
 
tdskip said:
Huh - I'm looking at my Bentley manual and it shows LG to #4.
Click to expand...

Tom,

Are you looking at the TR4 electrical diagram in the Bentley manual? Mine has a separate page for the TR4A electrical diagram and as Randall showed, nothing is shown connected to number 4. TR4A diagram is on page 28 in mine.

That L/G going to number 4 on the TR4 appears to have been replaced with a W going to number 2. Both go back to one of the fuses in the fuse box and appear to feed the lights, wipers, gauges, etc.

Scott
 
tdskip said:
OK - do here is the behavior I am seeing (which may/may not be related to my missing #4 post on the ignition switch).

I can use the solenoid to bump the engine over by using the manual switch in the engine bay, but turning the key doesn't result in anything.

When I put a test lamp on the white/red wire and turn the key it lights up when I turn the key all the way.

Ideas?
Click to expand...

Bad solenoid or bad ground for the solenoid? Can you feed power directly to solenoid and get it to engage/turn over?

Scott
 
Hi Scott!

So the solenoid will activate the starter when I press the button on the solenoid from the engine bay, so at least that part of it works.

Just seems odd that if that works the ignition key won't do the trick, especially when the white/red wire does get power when the ignition key is turned all the way....
 
I would check the white wire on the selenoid above the positive battery wire. its the one from the switch to the selenoid.
 
Hi John - that works, or at least it sends power when the ignition switch is turn to the crank starter position. It appears to be something inside the solenoid at this point... (to me anyway :laugh: )
 
Next I would apply power to that white/red small connection on the solenoid and see if that causes engagment.

As noted somewhere up there... the body of the solenoid has to be firmly grounded for it to work electrically -- to test this you could connect a jumper from a ground to the solenoid body then try the switch.
 
OK back - no dice. 12v applied to the post on the solenoid where the white/red wire goes does not excite the started.

If the solenoid works OK when the push button is depressed doesn't that indicate an OK ground? I don't think the ground path is different just because the white/red is being trigger via the ignition switch, does it?
 
tdskip said:
If the solenoid works OK when the push button is depressed doesn't that indicate an OK ground?
Click to expand...
No it doesn't. The "push button" on the solenoid operates the contacts directly, so no ground is needed. A burned out coil would cause the same symptoms.
 
Just guessing here...can that white/red wire terminal on the solenoid be isolated accidentally so that it doesn't get power? I vaguely remember something like that happening to me many years ago, but it could've been something else. (And, frankly, it's far too cold outside for me to run out to the barn and check!)
 
tdskip said:
Randall - any ideas on how to getter a better ground on the solenoid? Pull it and clean where it mounts?
Click to expand...
I would start by finding the bad connection : apply power to the side terminal and then use a test lamp or voltmeter first between the terminal and body. If you find power, the solenoid is bad. If not, check between the terminal and the head of one of the screws. If you find power now, then adding a lockwasher (preferably internal star type) under both screw heads should solve the problem.

But if the screw isn't getting grounded, then I would probably just add a ground lead from the solenoid to a convenient nearby point. The screws go into a spring clip and since it's unlikely the threads aren't making connection, the problem would have to be between the spring clip & the body. The alternative would be to remove the clip and sand away the paint around the hole, then smear a little Vaseline or grease on it (to prevent future corrosion) and reinstall the clip.

PS, In case it's not obvious, IMO it's more likely the solenoid is bad than it's not getting grounded.
 
Success!

The strap and screw that hold the solenoid in place corroded (she was stored for 20 years - a theme/prerequisite as it is turning out to end up in the "fleet") and that was enough to prevent it from working.

I took the strap and mounting post where the screw goes through back to bare metal, put on some dielectric grease, and she turns over like she should now.

Thanks guys - I <span style="font-weight: bold"><span style="text-decoration: underline">really</span></span> appreciate the info and coaching.
 
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